A Brief Introduction to Wavelength Selective Switch (WSS) of ROADM
Updated at Nov 13th 20241 min read
First-generation (Reconfigurable Optical Add-Drop Multiplexers) ROADMs relied on demultiplexer-switch-multiplexer technology or liquid-crystal wavelength blockers. Second-generation ROADMs utilized planar lightwave circuit technology, while today’s third-generation ROADMs are built on wavelength-selective switch (WSS) technology. WSS is essential in ROADMs, enabling dynamic routing of multiple wavelengths within a single optical fiber. This capability allows operators to swiftly adapt to changing traffic demands without the need for physical intervention. Let’s delve deeper into WSS and explore its importance in optical networks!
What Is WSS?
Definition of WSS
WSS is an essential component in wavelength division multiplexing (WDM) optical networks, enabling the routing of signals based on wavelength. It performs two primary functions: switching through port connections for each wavelength and adjusting power levels via attenuation. The hardware comprises an optics module and a control module, with a bulk diffraction grating facilitating simultaneous multiplexing and demultiplexing across multiple ports. Active elements, such as microelectromechanical systems (MEMS) mirrors or liquid crystal on silicon (LCOS) devices, alter the direction of incoming light beams. Each beam pathway varies by wavelength-port combination, necessitating careful design for stability and low loss. Additionally, the control module manages the switching element, detects faults, monitors operations, and provides a user interface for system interaction.
Figure1. WSS Working Principle
Source: WSS Module Technology for Advanced ROADM
Relation Between WSS and ROADM
The integration of Wavelength Selective Switches with ROADMs enhances the flexibility and adaptability of optical networks. ROADMs are vital in optical transport networks, enabling dynamic addition, removal, and routing of optical channels. By incorporating WSS modules, they gain the ability to selectively manage specific wavelengths of light, improving signal reconfiguration and grooming. This synergy provides network operators with precise control over optical traffic, facilitating efficient provisioning and restoration. Together, WSS and ROADMs form the foundation for flexible grid optical networks, optimizing wavelength allocation and spectral efficiency to meet diverse service demands.
Working Principle of Wavelength Selective Switch
The WSS integrates components like optical fibers, gratings, waveguides, and photodetectors to select specific wavelengths of optical signals through controlled diffraction. Here’s how it operates:
1. Incoming optical signals enter the WSS via optical fibers and proceed into the waveguide structure.
2. The signal is guided toward the grating within the waveguide.
3. The grating features periodic refractive index variations that enable the diffraction of different wavelengths by adjusting these variations.
4. Through this diffraction, specific wavelengths are selected and directed to their corresponding output ports.
5. Photodetectors measure the intensity of the optical signals at the output, allowing for precise control and adjustments.
6. Wavelength switching, multiplexing, and separation can be achieved by manipulating the grating's refractive index variations according to application needs.
The Role of WSS in Optical Networks
WSS are crucial for the development of flexible and adaptive optical networks. By integrating WSS technology into optical communication systems, network operators can manage wavelengths dynamically, leading to improved resource utilization and enhanced responsiveness to changing traffic patterns. This technology is vital for the adoption of software-defined networking (SDN) and network function virtualization (NFV), enabling the rapid allocation of optical resources and effective orchestration of optical services.
Furthermore, WSS is instrumental in the growth of high-capacity optical transport networks, allowing for the dynamic assignment and grooming of wavelengths to cater to varied service requirements. This adaptability is especially valuable in meeting the increasing demands for high-speed data transfer, cloud connectivity, and the needs of emerging 5G infrastructures. The utilization of WSS technology underscores its significance in promoting the efficient, scalable, and agile functioning of contemporary optical networks.
The ROADM-09T utilizes advanced WSS technology, providing exceptional flexibility by enabling dynamic routing of multiple wavelengths within a single fiber, which greatly reduces manual adjustments and operational costs. This ROADM’s flexible N*12.5GHz grid offers efficient add-drop and passthrough services, while built-in PA and BA ensure bidirectional signal quality. Meanwhile, FS also provides AmpCon™-T, a comprehensive management platform for centralized management, visual monitoring, and service configurations of the FS D7000 series (such as this WSS ROADM), enhancing efficiency and reducing costs.
Figure2. FS ROADM
Conclusion
In conclusion, the WSS in ROADMs is essential for improving optical networks, especially when integrated with ROADMs like the FS D7000 series ROADM-09T. This combination enables dynamic wavelength management and efficient signal routing, meeting the increasing demands for high-speed data transfer and diverse services, and paving the way for scalable and adaptive optical infrastructures crucial for modern networking.